Elastomeric compositions are used in a wide variety of applications, including hoses, belts, footwear components, vibration isolation devices, tires, and tire components such as treads, sidewalls, and innerliners. The selection of ingredients for the commercial formulation of an elastomeric composition depends upon the balance of properties desired, the application, and the application's end use. For example, in the tire industry the balance between processing properties of the green (uncured) composition in the tire plant and in-service performance of the cured rubber tire composite is of particular importance. An additional consideration to be balanced is the nature of the tire, e.g., bias versus radial tire or passenger car tire versus truck tire versus aircraft tire. The ability to improve a tire's air impermeability properties and flex fatigue properties without affecting the processability of the uncured elastomeric composition or while maintaining or improving the physical property performance of the cured elastomeric composition is a goal that still remains.
Generally, the raw ingredients and materials used in tire compounding impact tire performance variables. Thus, any alternative to conventional ingredients must be compatible with the rubbers, not interfere with the vulcanization rate, be easily dispersed in all tire compounds, be cost effective, and not adversely impact tire performance. This is of particular concern for tire innerliners and tire innertubes where performance properties must be maintained within specified tolerance levels. For example, small increases in a tire innerliner compound's 300% modulus can lead to reduction in fatigue resistance and cracks with consequential loss in tire durability. Furthermore, for an elastomeric composition that acts as an air barrier it is of particular importance that any benefits in compound processability are not to the detriment of the composition's air retention capabilities.
Conventionally, halobutyl rubbers have been used to obtain better air-retention in tires. While halobutyl rubber has allowed for improvement in a composition's air-retention qualities, it can negatively effect the composition's flex fatigue and brittleness properties. This is of particular concern for certain tire applications which require improved heat resistance and improved cold temperature properties, such as is required for race-car tires, snow tires, and aircraft tires. In order to improve flex fatigue and brittleness properties, secondary elastomers, such as ethylene-propylene rubber (“EP”), ethylene-propylene-diene rubber (“EPDM”), or natural rubber, have been blended with butyl rubbers in tire innerliner/innertube compounds. While these secondary elastomers may help improve flex fatigue and brittleness temperatures, the blending of EP, EPDM, or natural rubbers often increases the air permeability of the elastomeric composition.
Thus, there is still a need for an elastomeric composition that is suitable for a tire innerliner or tire innertube that will have enhanced thermal stability and physical properties under severe temperature and operating conditions such as required for race car tires and aircraft tires. It would be advantageous to have an elastomeric composition that possesses improved low-temperature toughness without sacrificing other advantageous traits such as improved processability and air-impermeability.